1. Field of the Invention
The present invention relates to valvular annuloplasty rings with enhanced biocompatibility and corrosion resistance. In particular, the invention relates to valvular annuloplasty rings constructed of zirconium oxide and zirconium nitride coated, low elastic modulus, metallic compositions.
2. Description of the Related Art
Valvular annuloplasty is a procedure for correcting deformities of the natural valves of the heart through implantation of a prosthesis, typically ring-shaped, which restores the shape of the deformed valve. Valvular annuloplasty is often utilized for correcting the tricuspid or mitral valves, although it is not restricted to those valves. Surgical alternatives to annuloplasty include replacement of the heart valve with a biological tissue valve or a mechanical valve.
Typical current annuloplasty rings are formed of a solid core, constructed from either a polymeric or metallic substance, with a woven polymeric sleeve or sheath, encasing the core. For example, U.S. Pat. No. 3,656,185 to Carpentier describes a ring core of stainless steel with a stitchable cord of polytetraflourethylene, both encased in a textile sheath, and U.S. Pat. No. 4,055,861 to Carpentier et al. describes an annuloplasty ring core constructed of a flexible biocompatible material enclosed in a textile sheath. U.S. Pat. No. 5,104,407 to Lam et al. describes a ring core made of a biocompatible material that is also antimagnetic, such as a cobalt-nickel alloy, with a knit polymeric outer sheath.
As with any surgical procedure, valvular annuloplasty faces complications that include malfunction of the ring due to distortion of the implant, physical or chemical deterioration of ring components, and tearing of the typical cloth sheath. The biocompatibility and physical characteristics (such as elasticity, strength, and wear resistance) of materials used in the annuloplasty ring components can be a factor in some of these complications.
Additionally, polymeric materials used in valvular annuloplasty constructs can degrade with time in the body. Water absorption and oxidation of the polymeric material can also adversely affect the material's properties, which can in turn lead to physical and structural alteration of the annuloplasty ring and adverse biological responses.
Metallic rings can experience damage of natural passive surface oxides via local movement of tissue or the sewing sheath. This local movement can produce metal ions, debris, and micro-electric currents which can adversely alter protein, tissue, platelet, and other cell attachments to the ring.
In an annuloplasty ring where the core is fabricated from a metallic element and the sewing ring or sheath is a polymer, there exists the possibility of metal ion release and micro-electrical (galvanic related) circuits due to abrasion between the polymeric sheath (also referred to as a sleeve) and metal core. The effect of metal ions and micro-electrical circuits on a biological environment is not entirely understood but it has been linked to adverse cellular, platelet, and protein response and the need for implant replacement.
Still needed in the art is a valvular annuloplasty ring construct with enhanced biocompatibility and elastic flexibility, having wear resistant surfaces with a subsequent reduction in metal ion release and reduced potential to create micro-electrical circuits.